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Conservator Masumi Takeuchi standing at a table holding a teflon folder while looking at a paper object
Visiting Conservator Masumi Takeuchi. 2024. Photo credit: Chloe Genter.

Crystals on Watercolor

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This is a collaborative post by Chloe Genter and guest author Masumi Takeuchi. Masumi is a conservator from Tokyo, working in private practice in Japan. She is currently a Visiting Conservator at the Library of Congress’ Conservation Division working on book and paper treatment projects.

Recently, a cartoon of a famous 19th century British jockey, Tom Loates from the Caroline and Erwin Swann collection of the Prints and Photographs Division at The Library of Congress received much needed treatment. Drawn in pencil on blue paper with watercolor washes in grey, red, white, blue and black, the cartoon is typical of the work of the artist and caricaturist, Sir Leslie Ward.

When Masumi received the drawing, it was attached to a poor-quality backing matboard and had thick adhesive along the edges on the recto side, suggesting that a window mat was adhered on top. The paper was also lightly discolored in the mat opening, and there were three horizontal brown stains in the upper section where the paper was more deteriorated and brittle. One of these stains that went through the drawing was a darker brown than the others and had a 7cm tear starting at the right edge that was bulging due to the partial detachment from the back board. The back board also had condition issues, as it was brittle overall, with dark brown stains and embrittlement in the same area of the stains on the blue paper. These stains were most likely caused by wooden slats when it was framed prior to coming to the Library.

Aside from the glaring discoloration of the board and adhesive residues, Masumi noticed the presence of clear crystals on the grey jacket of the figure in the areas where the paper was stained dark brown. When examined under a microscope, these crystals were tiny, clear, white particles which appeared to be in the fibers. Upon examination with ultraviolet (UV) illumination, the white trousers, white shirt, the bottom of the grey jacket, the red vest and the red helmet fluoresced suggesting the possible use of the pigment zinc white (zinc oxide). However, the areas where there were crystals did not fluoresce. The crystals were assumed to be some other form of a zinc salt, presumably from a reaction between the zinc white pigment, acidic degradation products from the backing board and wood frame, and a humid environment. The reaction of these materials seems to have resulted in “efflorescence”, the phenomena in which crystalline or powdery deposits of water-soluble salts appear on the surface of objects.

Three images side by side depicting close up shots of a white powdery substance resting on top of a grey surface
White crystalline efflorescence on the surface of the grey jacket taken before treatment. 2023. Photo credit: Masumi Takeuchi.

While the treatment that Masumi designed required removal of the backing board and the adhesive residues on the face of the drawing, she decided to treat the crystals first while the drawing was still mounted and provided some planar support. Since the crystals were fine particles and embedded into the fibers, it was difficult to remove them mechanically. The crystals appeared to be water soluble, so it was decided to dissolve them in water and absorb the dissolved solution. To do this, 6 % agarose gel was used to avoid the occurrence of tidelines and minimize any adverse effect on the watercolor. This was achieved by tiny pieces of agarose gel prepared with deionized water, which were placed on the crystals for 30 seconds to one minute in order to absorb the dissolved crystals in the gel. After removing the gel, the blue paper substrate was visible. What became apparent was most pigments were transformed when the efflorescence occurred and lost their color. As a result, Masumi decided to reduce the crystals but not remove them completely.

Five images side by side depicting close up shots of the white powdery substance on top of a brown background and a scalpel prodding the white substance. On the top row, the middle image shows the scalpel pointing to a square of agarose gel.
Left: The crystals on the surface, before treatment. Middle: During treatment, applying a piece of agarose gel under a microscope. Right: After removing the crystals, showing the blue paper substrate. 2023. Photo credit: Masumi Takeuchi.

Noninvasive analyses of the salt crystals was undertaken by the Preservation Research and Testing Division (PRTD) after the treatment of efflorescence was completed. When comparing the grey area to the other colored areas, the paper, and mat board, µXRF analysis detected a greater quantity of zinc. At the same time the white paint was identified as zinc oxide, and the presence of zinc in the grey paint was assumed to be an admixture of colors including zinc oxide. Sulfur was also detected in the paper and the increased proportions of zinc and sulfur in the crystalline deposits, suggesting formation of zinc sulfate salts. Raman spectroscopy analysis confirmed the presence of zinc sulfates in two different hydration states in the center lapel area of the jacket, which was treated with agarose gel prior to analysis.

Complementary µXRD analysis was conducted to obtain more definitive information on the identity of the crystals using micro-samples from the object. This analysis identified the presence of mixed metal zinc sulfate salts, including basic varieties in an area that was minimally treated with agarose gel. Colleagues in PRTD suggest that the slight moisture from the agarose gel treatment may have affected the original efflorescence and cause a reprecipitation of a purer zinc sulfate relative to the original zinc crystals.

To complete the treatment before returning it for storage to the Prints and Photographs Division, Masumi had to remove the adhesive and the backing board. She humidified the paper remnants on the front of the drawing with damp blotters and scraped off the softened adhesive, repeating this step several times until the final layer of adhesive could be removed with a soft damp cotton swab. The backing board was removed by trimming the board edges and then splitting it mechanically with a number of flat tools. Additional moisture was not added to remove the final layers of adhesive and paper of the backing board from the drawing to avoid the potential of further crystal formation. The remnants on the back were sanded lightly to create a planar surface. Finally, strips of Japanese mulberry paper tissue and wheat starch paste were used to reinforce the brittle, dark-brown stains in the middle of the drawing and to mend the 7 cm tear. After flattening the drawing under weight, it was housed in a window mat for storage and research.

Additional treatment of the zinc sulfate crystals was not conducted, as it had become apparent that the transformation of the zinc white or zinc oxide pigment into the clear crystalline zinc sulfates resulted in loss of the painted color. Removing the crystals completely or leaving them undisturbed would result in disfiguration of the drawing. Masumi chose a conservative approach, that is, minimizing the chemical or physical intervention of the object, and reduced the crystals in such a way that they are no longer noticeable—and the drawing can be enjoyed without a gleam or a sparkle!

All in all, this treatment was extensive yet achieved good results…

Two images side by side of the cartoon before and after treatment. The left shows a man with hands on hips, surrounded by peeling and yellowed board material. The right depicts the same image with the peeling and yellowing removed.
Left: The cartoon of famous 19th century British jockey, Tom Loates before treatment. Right: The cartoon after treatment. 2023. Photo credit: Masumi Takeuchi.
Two images side by side, depicting round grey circles with the white powdery crystals resting on top.
A close up of the crystals on the surface. Left: Before treatment close up. Right: After treatment close up. 2023. Photo credit: Masumi Takeuchi.

…and overall it improved the condition of the drawing.

This post was written by Masumi Takeuchi while working at the Library of Congress as a Visiting Conservator. She had heard wonderful things about the Library from colleagues in Japan, and has since returned to the Library after her mid-career internship in 2015-2016. In her spare time, Masumi enjoys horseback riding with her husband in Virginia. She also loves to bake her favorite Japanese delicacies at home.

 

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